1. Field of the Invention
The invention relates to wells and, more particularly, to grapples or extractors for withdrawing downhole objects. The object(s) of specific interest herein is the well casing typically comprising a downhole hollow tubeform, nowadays commonly an assembly of PVC pipe sections which twist together with counterpart internal and external threaded ends. The conventional occasion nowadays for wanting to withdraw such a casing out of the well is typically during the abandonment (decommissioning) of environmental monitoring wells.
2. Prior Art
FIGS. 1 and 2 show various aspects of the prior art which will be more particularly described next. Brief pause can be taken now to consider the background behind.
At some earlier time, groundwater monitoring/remediation wells are bored into the earth. An undersized casing is inserted into the bore hole about all the way to the bottom. Typically the casing comprises an assembly of PVC pipe sections which are twisted together with counterpart internal and external threaded ends to form a sealed casing as a whole. It is preferred to avoid use of adhesive to join together the joints in the PVC pipe assembly (or in the role of adding a further assurance that threaded joints remain joined) because the adhesive or any other chemical or compound that is likely to be utilized could leach or partially dissolve, thereby showing up as a contaminant and thereafter skewing/undermining the monitoring/remediation efforts.
Again, the casing—typically an assembly of PVC pipe sections twisted together by the counterpart internal and external threaded ends thereof—is undersized: —relative that is to the bore hole in which it is inserted. Thus such an undersized casing presents an annular gap between the bored earth and PVC pipe. This annular gap is backfilled. About the lowest ten feet (˜3 m) or so is backfilled with sand, the remaining depth (dozens or hundreds of feet or meters) is backfilled with cement or the like, bentonite being a common substitute. Also, the lowest ten feet (˜3 m) or so of the PVC pipe is produced as a screen (eg., perforated) to allow groundwater to seep in.
The foregoing describes what occurred a month to a decade earlier than the time with which the present invention is concerned. That is, to come forward to the present problem, there comes a time to abandon (decommission) the well. Regulatory authorities want the (PVC pipe) casing pulled all the way out, and the remaining bore sealed in with cement. If the (PVC pipe) casing is left in place downhole, there will always be a danger that polluted groundwater from a relatively higher substratum elevation might weep down the outer skin of the (PVC pipe) casing, because the cement (or the like) backfill fails to form a perfect seal, until the weeping-down polluted water contaminates groundwater in lower substratum levels.
To turn to another matter of the prior art, there is another piece of the background to note, which involves the field equipment used by the workers in this industry: —eg., their drilling rigs. Namely, such drilling rigs have two kinds of devices for retracting downhole tools: —ie., hydraulically-winched cables or lines in contrast to hydraulic cylinders.
It might be noted that hydraulically-winched cables and lines, when used to pull free a stuck object, typically include the danger of recoil. Conversely, hydraulic cylinders are essentially recoilless in the same situation. Also, the hydraulic-cylinder systems of such drilling rigs are powerful, and typically outmuscle the power of the hydraulic winches by several times.
A typical drilling rig utilized in the industry might comprise, for example and without limitation, a CME 750 All-terrain (rubber tire) vehicle drilling rig of the Central Mine Equipment Company in St. Louis, Mo. This is the carrier/drilling rig combination which is approximately illustrated in the drawings. More particular reference can be had to several patents of the CME Company for more particular disclosure of carrier/drilling rig features, including any of U.S. Pat. Nos. 3,527,309; 3,561,545 and/or 4,638,871—all of which are by C. L. Rassieur. The foregoing patent disclosures are incorporated fully herein by this reference thereto.
Such a carrier/drilling rig has a two-piece tower comprising, in the lower portion thereof, an undergirding upright, upon which is affixed a removable mast. The crown of the mast might be outfitted with as many as five sheaves. In a five sheave configuration, typically one sheave serves a wireline cable and winch, another serves softlines perhaps pulled by a cathead, and the remaining three would typically serve three cable-and-winch systems for winching up (eg.) sections of drill rod. The wireline cable and softline-cathead system are not pertinent to the present invention. Typically the wireline cable system reels up a wire relatively fast but with a weak hoist (eg., able to exert 900 pounds or ˜400 kg of force or so) and is utilized in rock-coring, for example. The cathead is like a capstan on a ship, except oriented on a horizontal turning axis, and can winch in by means of one or two loops not only softlines but also cables and/or chains as well. It typically is a weak system too.
Stronger still are the (three or so) cable-and-winch systems. It is typical to equip the drilling rig with winches rated between about 1,800 or to 3,200 pounds (˜700 to ˜1,400 kg). It is also known to include at least one cable-and-winch system as a main one for fishing stuck objects and the like, and provide it with a retraction-force rating as high 10,000 pounds (˜4,500 kg). Again, these three cable-and-winch systems are designed for, among other end uses, lifting up sections of drill rod. The height of the tower to the crown of the mast is typically something greater than twenty feet (˜6 m) since that is a standard length of sections of drill rod. The above-ground height of the sheaves for the CME 750 ATV is about twenty-seven and a-half feet (˜8⅓ m), which means that workers can hoist the twenty-foot rods with clearance to spare. When the CME 750 ATV is equipped with three such hoists (ie., cable-and-winch systems), workers can pull sixty feet of rods without having to lay any down on the ground or on the deck.
The upright (again, which undergirds the detachable mast) comprises legs and a standing rotary drive shaft (eg., a kelly bar, sometimes a square bar). The standing rotary drive bar typically has a lower end anchored in a main rotary drive and an upper end held in a bearing. The legs carry between (or among) themselves a traveling rotary table. Drive input to the rotary drive table is received from the standing rotary drive shaft as the traveling rotary table transits up and down the standing rotary drive shaft. The drill drive is typically a pair of serially-suspended links interconnected by a U-joint.
The hydraulic vertical drive system for cycling the traveling rotary drive table between feed (eg., pulldown) and retraction strokes typically comprises hydraulic cylinders which serve double-duty as the legs for the upright. The main rotary drive and the hydraulic vertical drive system are typically the strongest systems on the carrier/drilling rig. That is, the main rotary drive might deliver 10,000 ft-lbs (˜13,5000 Nm) of rotary torque. The hydraulic vertical drive system can typically deliver a feed (pulldown) force in excess of the weight of the vehicle, or something on the order of 20,000 pounds (˜9,000 kg).
The outstanding feature of the hydraulic vertical drive system is the retraction force it can develop: —30,000 pounds (˜13,600 kg) for the CME 750 ATV, and then 40,000 pounds (˜18,000 kg) being no problem for other models.
As an aside, another aside, another aspect of the hydraulic vertical drive system is that its drive stroke is only about five and a-half feet (˜1⅔ m) in order to provide sufficient clearance for drills or augers, which conventionally are a standard five feet (˜1½ m) in length.
More importantly, the hydraulic vertical drive system has no cables which can stretch (nor chains which need lubrication). Better yet, the hydraulic vertical drive system is substantially recoilless. When feeding down or retracting up against a stuck object, as soon as the sticking force is overcome the hydraulic vertical drive system does not recoil. In contrast, cables stretch or the stuck object (if being retracted up) can let fly after being unstuck (or after being torn apart), chains can whip and so on. Moreover, cables can snap, so can chains. Accordingly, the hydraulic vertical drive system gives precise control over the force applied to downhole tools or objects.
Arguably most significant of all is that, its brute power aside and in spite of being the most powerful system on the carrier/drill rig, the hydraulic vertical drive system is probably the safest.
Now let's return the discussion back to the present problem. The prior art conventionally extracts (PVC pipe) well casing with a grapple that engages the casing at the very bottom of the well. The grapple is fed down by winch and cable, and likewise hoisted up by the same winch and cable. For example, the prior art U.S. Pat. No. 6,615,919—Osgood et al., shows a knurled brass cylinder. The foregoing patent reference is incorporated herein by this reference thereto. It is also approximately illustrated in FIG. 2 hereof. Although the device of Osgood et al. has a solid shaft on the top, the shaft is short and so a cable is hooked to an eye on top of the shaft. The winch thus lowers the knurled brass cylinder the dozens (or hundreds) of feet by way of the cable all the way to the bottom of the well. Sand is poured in from the well head atop the cylinder to force wedging between the casing and cylinder.
To pull the casing, workers have to repetitively task through this exercise. That is, the winch is operated to reel the cable in as it courses over a sheave at the crown of the mast, about twenty-five feet (˜11 m) above ground level. All the while, the workers have to be slitting the casing along an axial run along the sidewall. This is proposed to be done by a portable reciprocating power saw. At a time when twenty feet or so of the casing is withdrawn, then the workers have to stop because the casing is about to hit the sheave at the crown of the mast. The workers then cut-off the withdrawn twenty-foot section casing. Since the cut-off portion of the casing is also slit, then it has to be peeled off the cable in order to displace it free of the cable.
Then the workers can withdraw a fresh new twenty foot section of the casing, slitting it's sidewall all the while, stop, cut-off at ground level, peel-off too, and so on repetitively until the entire casing is withdrawn this way.
The foregoing has shortcomings. The winches are often underpowered for the task. Moreover, to cause the casing to release from its concrete backfill there is oftentimes a considerable pulling force applied, and the cable is considerably stretched. When the casing does break free, things fly. The casing is likely to shoot up like a projectile, the cable is likely to relax and whip around. It is a dangerous moment. Also, if the cable breaks or the grapple is irretrievably caught, then there are no practical options for fishing out the grapple, and so the well is abandoned as is, and with the grapple and (PVC pipe) casing in place. Additionally, the task of splitting the PVC pipe along the axial length thereof in runs of twenty-foot sections is slow work. Care must be exercised not to damage the saw, not to mention the cable.
What is needed is a solution to overcome the shortcomings of the prior art.